Ah yeah the Metal Lube Bucket does not exist, that is the Issue with Vanilla Buckets, there has to be one Item for each Fluid Block, and ONLY one Item, not two or three, which is why I do not add Vanilla Bucket Variants for my Fluids. Well that and I did not add a Lube Fluid Block either, but I think Immersive Engineering does.
Edit: that said, Glass Bottles are fine if there is multiple so I did add a Glass Bottle variant, which also wastes less Lube when used in Crafting, than a Bucket.